Added messages for BatteryTag implementation

[tridge]

added GlobalTime and BatteryTag messages

see ArduPilot/ardupilot#29310 for implementatin

[hendjoshsr71]

BatteryPeriodic contains nearly all of the battery tag fields.

Is there a way we can use that message here?
I’d love to hear about the use case.

Most of the additional fields seem to me of minimal importance. I’d hate to see folks only implementing one message vs another.

The real questions are how do various fields transfer to estimated SOC & SOH. Aka current estimated capacity at a given discharge rate that help estimation of flight times.

time armed isn’t super useful imo since that could be discharging at crazy rates or discharging at near 0 amps.

Time of first use or since most recent at armed seem to me to be meaningless to the computation of SOH or SOC

• how many mAh is fully charged
• How many mAh do we think is left given the current discharge rates

It’s unfortunate there is no way to add extensions on dronecan.

[tridge]

I’d love to hear about the use case.

the use case is AP_Periph nodes permanently attached to the battery. The node does not measure voltage/current etc, it is just a way to persistently store information on when the battery came into service, how many cycles it has done etc. This is not for a smart battery, it is for a normal LiPO that has this tag attached.
The BatteryPeriodic message is not a good match